U.S. Pat. No. 5,440,987, U.S. Pat. No. 5,206,102, U.S. Pat. No. 5,816,161, U.S. Pat. No. 5,379,693; U.S. Pat. No. 6,779,449; U.S. Pat. No. 6,424,366, U.S. Pat. No. 6,190,828, EP 1188579 and EP 1495877 disclose imaging techniques.